A known method of manufacturing a gear utilizes a skiving process. The skiving process will be explained as follows with reference to FIG. 1. While being rotating in synchronization with a work to be processed into the gear, a pinion cutter (hereinafter referred to as a cutter) is fed in a tooth trace direction of each of teeth to be formed at the work. The cutter has a rotational axis inclined relative to a rotational axis of the work. Here, the skiving process is a gear cutting process in which the cutter is fed from an upper side to a lower side along the rotational axis of the work to thereby form the teeth of the gear on a work surface of the work.
In the skiving process, the work is cut by the cutter with slippage generated between the cutter and the work rotating in synchronization with each other; therefore, the work may be smoothly cut by the cutter compared to a case where a work is cut by a simple reciprocating movement of a cutter. In addition, according to the known method, the rotating speed of the cutter is increased in the skiving process; thereby, the work may be easily cut at high speed. Therefore, the skiving process is effective to process the work into the gear (for example, a strain wave gearing) that has multiple minute teeth.
In the skiving process, the work is cut by the cutter while being rotated in synchronization with the cutter as described above. Accordingly, for example, as illustrated in FIG. 9, when tooth grooves 12 are being formed at a work 10 (to be processed into the gear) by cutting blades 2 of a cutter 1, each of the cutting blades 2 moves relative to the work 10 from a position T1 through positions T2, T3, and T4 to a position T5. When the cutter 1 rotates from the position T1 to the position T2, from the position T2 to the position T3, and from the position T3 to the position T4, the cutting blade 2 makes contact with the work 10. Thereafter, when the cutter 1 rotates from the position T4 to the position T5, the cutting blade 2 separates from the work 10. During the time when the cutting blades 2 make contact with the work 10 to the time when the cutting blades 2 separate from the work 10, the cutting blades 2 are cutting the work 10.
As illustrated in FIG. 9, during the cutting process of the work 10, a burr B is generated on a work surface of the work 10 in a direction in which the cutting blades 2 separate from the work 10. The rotation of the cutting blades 2 is repeated; thereby, the tooth grooves 12 are formed in the work surface of the work 10. As a result, the multiple burrs B are generated on the work surface along a tooth trace direction of each of teeth 11 to be formed at the work 10. In addition to the burrs B generated by the rotation of the cutter 1, in a case where the cutter 1 separates from the work 10 in accordance with the feed motion of the cutter 1, burrs are generated on a portion of the work surface, the portion being located at a lower side of the feed direction of the cutter 1.
In a general process for manufacturing a gear, a work surface of a work to be processed into the gear is cut by a cutter; thereby, teeth of the gear are formed at the work surface. Afterward, a finishing process or a thermal process is applied to the work surface. At this time, burrs generated on the work surface are removed therefrom. However, in the case of processing the gear such as the strain wave gearing that has the minute teeth, the minute teeth formed at the work surface may be damaged or deformed by the finishing process or the thermal process. Therefore, the finishing process or the thermal process is not often applied to the minute teeth. In such case, the burrs generated when the work is cut by the cutter needs to be minimized.
A need thus exists for a method of manufacturing a gear, which is not susceptible to the drawbacks mentioned above.